My cat is having clear liquid accidents?

i have a cat that was a stray. she is young and just had a litter of 3 kittens 3 weeks ago. the kittens are happy and healthy. she has been fine through the whole thing. however today when i went to check on them the blanket was wet and her backside was soaked. i cleaned her up and the mess and a few hours later she did it again. its clear and it smells bad like feces. what could this be? and could the kittens be in danger?